Optical communications networks, at one time, were generally “point to point” type networks including a transmitter and a receiver connected by an optical fiber. Such networks are relatively easy to construct but deploy many fibers to connect multiple users. As the number of subscribers connected to the network increases and the fiber count increases rapidly, deploying and managing many fibers becomes complex and expensive.
A passive optical network (PON) addresses this problem by using a single “trunk” fiber from a transmitting end of the network, such as an optical line terminal (OLT), to a remote branching point, which may be up to 20 km or more. One challenge in developing such a PON is utilizing the capacity in the trunk fiber efficiently in order to transmit the maximum possible amount of information on the trunk fiber. Fiber optic communications networks may increase the amount of information carried on a single optical fiber by multiplexing different optical signals on different wavelengths using wavelength division multiplexing (WDM). In a WDM-PON, for example, the single trunk fiber carries optical signals at multiple channel wavelengths to and from the optical branching point and the branching point provides a simple routing function by directing signals of different wavelengths to and from individual subscribers. In this case, each subscriber may be assigned one or more of the channel wavelengths on which to send and/or receive data.
To transmit and receive optical signals over multiple channel wavelengths, the OLT in a WDM-PON may include a multi-channel transmitter optical subassembly (TOSA), a multi-channel receiver optical subassembly (ROSA), and associated circuitry. The OLT module may also include other components such as a thermoelectric cooler (TEC), TEC controller, microcontroller, and heaters for wavelength control. One challenge with such OLT transceiver modules is accommodating the multi-channel TOSA, ROSA and circuitry in the relatively small space available in an OLT module while allowing the desired temperature control and thermal management. In a multi-channel transceiver, for example, the multiple lasers and photodiodes are electrically connected to circuit components, such as integrated circuits, which require space within the transceiver housing. The multiple lasers and photodiodes also generate heat, which may adversely affect operation of the transceiver if the heat is not properly dispersed.